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Bad timing or what?

N

Norwegian

NAXJA Forum User
Location
Norway
Not sure how to explain this but i'll give it a shot..

My '90 4.0 XJ runs pretty good but it feels like the timing's a bit advanced (?)
The first touch of the gas pedal will make it jerk and accelerate way harder than i'd want. This makes is a nightmare to wheel when i need crawl speed control over hard obstacles.
There's no smooth transition however gently i touch the accelerator, it just leaps forward.

Some b.s. sensor issue or is this something i can tune?
 
Worn out TPS (Throttle Position Sensor) will do that.
 
kdailey4315 said:
You have an adjustable TPS. Try adjusting it before you shell out the coin for a new one.
Click to expand...

Good point. I forgot the 1990 was still renix. :thumbup:
 
kdailey4315 said:
You have an adjustable TPS. Try adjusting it before you shell out the coin for a new one.
Click to expand...

Great! Any input on how to do that? I have the 1990 FSM but it says nothing on adjusting the TPS just that it puts out 1-5V..
Would i be adjusting the TPS arm on the throttle body?
 
Power off test the ground wire on the TPS to the battery negative post, make sure it is less than 1 ohm. If it is high, like over 3 ohms, fix it first. Then, engine off, ignition in the run position, loosen the TPS mounting screws, adjust the sensor to read .82 volts, then tighten the mounting screws. Then using a high impedance analog volt meter (needle style), slowly move the throttle from idle to wide open throttle (WOT), and back to idle, and look for a spot where the needle jumps. IF the needle jumps, or has a flat spot where the resistance does not change smoothly while the throttle moves, the TPS is bad.

Yours sounds like it is jumping around near the current idle spot, indicating it is worn and giving a bad signal near idle on take off.
 
Another issue just popped uo today as i was messing around with the jeep.

If i crawl real slow or idle forward with some resistance so the revs get real low like 2-400rpms and push the clutch the engine will rev up to 1600-2200 rpms depending on how hard i've pushed it.

Why?? would this contribute the the shitty idle/clutch control i have?
 
Is you foot on the gas peddle at all during that period?
 
cruiser54 said:
Also indicative of a faulty TPS.
Click to expand...

Or a sticky IAC? Or a bad connection for the TPS to the ECU. I even had a random high idle that was bad IAT sensor, that confused the ECU enough to set off random high idles in park / neutral.


Norwegian,

Get a copy of the Renix Fuel Injection manual (PM me an email if you need a copy) and a volt / ohm meter and test all the sensors for Factory specs.
 
Thanks again.

Worth a try for sure. It idles ok but everytime i start it up it revs up quote a bit before settling down.
I'm gonna clean the IAC and the throttle body thoroughly, iirc it looks like crap in there.

I really need this thing running right to stand a chance in the upcoming events..
 
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